全文获取类型
收费全文 | 120814篇 |
免费 | 778篇 |
国内免费 | 840篇 |
专业分类
电工技术 | 2527篇 |
综合类 | 139篇 |
化学工业 | 16287篇 |
金属工艺 | 10114篇 |
机械仪表 | 7381篇 |
建筑科学 | 2265篇 |
矿业工程 | 955篇 |
能源动力 | 2102篇 |
轻工业 | 3478篇 |
水利工程 | 1498篇 |
石油天然气 | 2851篇 |
无线电 | 11459篇 |
一般工业技术 | 31253篇 |
冶金工业 | 13437篇 |
原子能技术 | 1908篇 |
自动化技术 | 14778篇 |
出版年
2021年 | 340篇 |
2019年 | 374篇 |
2018年 | 9725篇 |
2017年 | 10397篇 |
2016年 | 5804篇 |
2015年 | 1111篇 |
2014年 | 898篇 |
2013年 | 2442篇 |
2012年 | 4214篇 |
2011年 | 10755篇 |
2010年 | 10064篇 |
2009年 | 9034篇 |
2008年 | 8629篇 |
2007年 | 10945篇 |
2006年 | 1479篇 |
2005年 | 5143篇 |
2004年 | 3358篇 |
2003年 | 2846篇 |
2002年 | 1779篇 |
2001年 | 1185篇 |
2000年 | 1107篇 |
1999年 | 1021篇 |
1998年 | 2120篇 |
1997年 | 1659篇 |
1996年 | 1454篇 |
1995年 | 994篇 |
1994年 | 788篇 |
1993年 | 801篇 |
1992年 | 614篇 |
1991年 | 596篇 |
1990年 | 524篇 |
1989年 | 485篇 |
1988年 | 376篇 |
1987年 | 402篇 |
1986年 | 363篇 |
1985年 | 381篇 |
1984年 | 305篇 |
1983年 | 300篇 |
1982年 | 301篇 |
1981年 | 296篇 |
1980年 | 349篇 |
1979年 | 341篇 |
1978年 | 294篇 |
1977年 | 415篇 |
1976年 | 629篇 |
1975年 | 308篇 |
1974年 | 292篇 |
1973年 | 311篇 |
1968年 | 318篇 |
1966年 | 277篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
991.
A series of polyesters was prepared to evaluate hydrolytic stability as a function of cyclohexyl dibasic acid content. The
three cyclohexyl dibasic acids: 1,2; 1,3; and 1,4 were formulated into polyesters with two glycols. The proportion of cis
and trans isomers was evaluated via 1H NMR. The hydrolytic stability of short chain polyesters was evaluated in an acetone/water mixture which solubilized the
polyesters to mimic oligoester behavior within a thermosetting polyester coating environment. The rate of hydrolysis was monitored
by acid titration and corroborated by GPC. Surprisingly, 1,2-cylohexyl diacid-based polyesters were robust, and 1,3-cyclohexyl
diacid-based polyesters were the most susceptible to hydrolysis. Evidently, a 1,2-anchimeric effect for cyclohexyl dibasic
acid polyesters was not an important consideration, while the 1,3-cyclohexyl ester interaction was. Consequently, an anomeric
effect was proposed.
Presented at the 81st Annual Meeting of the Federation of Societies for Coatings Technology, November 12–14, 2003, in Philadelphia,
PA. 相似文献
992.
A monolayer and a few layers of carbon sp2-bonded networks were torn and folded by the tip of an atomic force microscope at the steps on newly cleaved highly oriented pyrolytic graphite. It was found that the preferential breaking directions and folding axes are along the symmetry directions of the graphite hexagonal structure. Depending on the force exerted by the tip, breaking may occur along other directions. The torn part of the graphene sheet can even be stretched and deformed, and does not resume its original shape after release from the tip. 相似文献
993.
The dependence of carrier density in silicon quantum wires sheathed with SiO2 on the wire diameter and the position of impurity atoms in respect to the wire center is analyzed theoretically. It is shown that, as the diameter of wires and nanocrystals decreases, the ionization energy of a dopant increases; therefore, the free carrier density decreases, and the screening of the Coulomb attraction becomes ineffective. As a result, the photoluminescence is defined by the radiative recombination of excitons even in the case of heavily doped Si. These conclusions are supported by the data of experimental study of spectral, excitation-power, and temperature dependences of photoluminescence in porous silicon structures fabricated on lightly and heavily doped Si substrates. 相似文献
994.
995.
Soft X-ray emission from the plasma of a conductor exploding in a strong longitudinal magnetic field
Previous experiments with the electric explosion of conductors in a strong (50 T) longitudinal magnetic field showed the formation
of a relatively low-density plasma around the central part of the explosion channel, which exhibited expansion at a velocity
on the order of 10–20 km/s [1, 2]. Expansion of the plasma was accompanied by displacement of the magnetic field from the
explosion channel, which was manifested by a diamagnetic signal. An analysis of the plasma energy balance is hindered by the
lack of reliable data about radiative energy losses. Here, we report the first experimental results on the radiation pulse
kinetics and the first estimates of the radiation energy. 相似文献
996.
An NMR tracking magnetometer, in which the frequency modulation is used instead of the traditional magnetic modulation, is described. Owing to the proposed digital compensation of modulation shifts, the tracking error is negligibly small and does not exceed the corresponding error for NMR magnetometers with magnetic modulation. The absence of the modulation rings decreases the sizes of the sensors to the utmost and excludes their effect on the surrounding systems. 50%-deuteron saturated solution of lithium chloride in water of 50% deuterons, which is used as a sensor substance, allows one to measure magnetic fields of 0.0625 to 15.3 T with a 10?7 relative error at the most. 相似文献
997.
Barbara K. Reck Robert B. Gordon 《JOM Journal of the Minerals, Metals and Materials Society》2008,60(7):55-59
Nickel and chromium are essential ingredients in alloys increasingly important for energy-efficient, environmentally friendly
modern technology. Quantitative assessment of the flows of these metals through the world economy from resource extraction
to final disposal informs resource policy, energy planning, environmental science, and waste management. This article summarizes
the worldwide technological cycles of nickel and chromium in 2000. Stainless steel is the major use of these metals, but they
serve numerous other special needs, as in superalloys for high-temperature service, as plating materials, and in coinage.
Because they are used primarily in alloys, novel recycling issues arise as their use becomes more widespread.
“... the great New York and St. Louis double track, nickel plated railroad...”
— Norwalk, Ohio, Chronicle 10 March 1881 announces arrival of surveyors for the future Nickel Plate Railway
“Later [1911] I formed an alloy of Iron and Chromium, which showed remarkable resistance to rust and tarnish ... [It was]
rediscovered by an Englishman named Brearley, in 1914.”
—Elwood Haynes to Stephen F. Roberts, 17 January 1925 相似文献
998.
Results from an investigation into combustion of wooden and charcoal particles at relatively low temperatures are presented. Combustion modes are determined, and the effect the fuel reaction properties have on the thermal treatment and combustion process is evaluated. The results are compared with well-known figures on fossil fuels and with the data calculated using the classic diffusion-kinetic model. 相似文献
999.
E. M. Kozulin A. A. Bogachev M. G. Itkis I. M. Itkis G. N. Knyazheva N. A. Kondratiev Ľ. Krupa I. V. Pokrovsky E. V. Prokhorova 《Instruments and Experimental Techniques》2008,51(1):44-58
The CORSET time-of-flight spectrometer has been developed at the Flerov Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research (Dubna, Russia) for investigating binary products of nuclear reactions. The spectrometer has been used to study the dynamics of fusion-fission and quasi-fission of superheavy elements. The design and the main characteristics of the spectrometer, as well as the algorithms for deducing the mass-energy distributions of fragments and the cross sections of nuclear reactions, are presented. The spectrometer contains two time-of-flight arms based on microchannel-plate detectors and three telescopes, each of which is composed of two microchannel-plate detectors and one semiconductor detector. A system of four semiconductor detectors is used to obtain the absolute value of a cross section. The time resolution of the time-of-flight arms is 150 ps, which allows the time-of-flight distances to be set at 10–20 cm, thus providing a mass resolution of 3 amu and an angular resolution of 0.3°. Owing to these characteristics, the spectrometer can be used as a trigger in multidetector setups for measuring light charged particles, neutrons, and γ rays in coincidence with reaction fragments. 相似文献
1000.
Shafeeque G. Ansari Mushtaq Ahmad Dar Young-Soon Kim Hyung-Kee Seo Gil-Sung Kim Rizwan Wahab Zubaida A. Ansari Jae-Myung Seo Hyung-Shik Shin 《Korean Journal of Chemical Engineering》2008,25(3):593-598
A comparative study for the nucleation of diamond was carried out using surface treatment like (i) surface scratching with
1 μm diamond paste and (ii) surface etching using chlorine plasma at different RF powers (50, 100 and 150 W). Atomic force
microscopic study shows variation in roughness from 31 nm to 110 nm. Scratching results in random scratches, whereas plasma
etches a surface uniformly. Scanning electron microscopic observations show well faceted crystallites with a predominance
of angular shaped grains corresponding to 〈100〉 and 〈110〉 crystallite surfaces for the scratched as well as plasma etched
substrate. Surface etching at 150 W plasma power results in a better growth in comparison with 50 and 100 W plasma powers.
Chlorine-radical is found responsible for the changes in the growth morphology. Raman spectroscopy shows a sharp peak at 1,332
cm−1 and a peak at ∼1,580 cm−1 for both samples. 相似文献